Key telephone transmission system

• US 4,583,214 A
• Filed: 03/16/1984
• Issued: 04/15/1986
• Est. Priority Date: 03/17/1983
• Status: Expired due to Fees

• Current Assignee: Iwasaki Tsushinki Kabushiki Kaisha A Joint Stock Company of Japan
• Original Assignee: Iwasaki Tsushinki Kabushiki Kaisha
• Inventors: Miyashita, Hiroyuki, Kawata, Yoshihiro, Hirato, Akira
• Primary Examiner(s): Olms, Douglas W.
• Application Number:
  US06/591,191
• Time in Patent Office: 760 Days
• Field of Search: 370/5, 179/99 R, 179/99 LC, 179/99 LS, 179/99 M
• US Class Current: 370/200
• CPC Class Codes: H04L 5/20 using different combinations of lines, e.g. phantom working
• CPC Class Codes: H04M 9/003 Transmission of control signals from or to the key telephone set; signalling equipment at key telephone set, e.g. keyboard or display equipment keyboard equipment in semi-automatic systems H04M3/62

Abstract

A transmission system for a key telephone system, in which speech signals and control signals are transmitted through two pairs of transmission conductors between a key service unit and each of a plurality of key telephone sets, and in which DC electric power is supplied from the key service unit to each of a plurality of telephone sets. In accordance with the present invention, the speech signal and the control signal are transmitted through a first transmission line of high frequency band provided by one pair of the transmission conductors from the key telephone set to the key service unit, and the speech signal and the control signal are transmitted through a second transmission line of high frequency band provided by the other pair of the transmission conductors from the key service unit to the key telephone set. A third transmission channel is provided by the use of respective neutral points of the two pairs of transmission conductors established at the key service unit and by the use of respective neutral points of the two pairs of transmission conductors established at the key service unit to form a voice-frequency two-way transmission line between the key service unit and the key telephone set. DC electric power is supplied from the key service unit to the voice-frequency two-way transmission line from a DC power source, so that the DC electric power supplied is separated from the voice-frequency two-way transmission line by a power separating circuit, such as a smoothing circuit.

Claims

1. A key telephone transmission system provided between a key service unit, and a respective key telephone set, comprising:

a first transmission line of high frequency exceeding a voice frequency band provided as one pair of transmission conductors, a first transformer having a secondary winding connected at the key telephone set to the one pair of transmission conductors, and a second transformer having a primary winding connected at the key service unit to the one pair of transmission conductors so as to couple to the first transformer through the one pair of transmission conductors;

a first transmission circuit at the key telephone set connected to the primary winding of the first transformer for transmitting a speech signal and a control signal from the key telephone set to the key service unit;

a first receiving circuit connected at the key service unit to a secondary winding of the second transformer for receiving the speech signal and the control signal transmitted from the key telephone set;

a second transmission line of high frequency exceeding a voice frequency band provided as another pair of transmission conductors, a third transformer having a secondary winding connected at the key service unit to said another one pair of transmission conductors, and a fourth transformer having a primary winding connected at the key telephone set to said another one pair of transmission lines so as to couple to the third transformer through said another one pair of transmission lines;

a second transmission circuit connected at the key service unit to the primary winding of the third transformer for transmitting a speech signal and a control signal from the key service unit to the key telephone set;

a second receiving circuit connected at the key telephone set to a secondary winding of the fourth transformer for receiving the speech signal and the control signal transmitted from the key service unit;

a third transmission line of voice frequency band and power supply provided by a fifth transformer and a sixth transformer, a secondary winding of the fifth transformer being connected to respective neutral points of the primary winding of the second transformer and the secondary winding of the third transformer, a primary winding of the sixth transformer being connected to respective neutral points of the secondary winding of the first transformer and the primary winding of the fourth transformer;

a first talking circuit connected at the key service unit to a primary winding of the fifth transformer;

a second talking circuit connected at the key telephone set to a secondary winding of the sixth transformer;

DC power supply means included in the secondary winding of the fifth transformer to supply DC electric power to the key telephone set; and

DC power separating means included in the primary winding of the sixth transformer to separate the DC electric power supplied from the DC power supply means.

2. A key telephone transmission system according to claim 1, in which the first transmission circuit and the second transmission circuit apply the speech signal having a PCM digital signal format at the first transmission line and the second transmission line respectively.